Demo on actionButtons, reactiveValues and Sys.sleep()

server.R

# server.R

shinyServer(
  function(input, output, session){
    
    # Part I: create an observer on the state of actionButton "calculate"

    busy <- reactiveValues(state = 0)
    
    observe({ 
      if(is.null(input$calculate) || input$calculate == 0){return()} 
      busy$state <- 1 - isolate(busy$state) # toggles between 0 and 1
    }) 


    # Part II: create an observer on the reactiveValues based on the state of actionButton "calculate"
    # Alternatively, nest the conditionals inside output$observeReactiveValues with a return() for each branch

    observe({
    
        input$calculate
    
        # if input$calculate is undefined, e.g. wrapped in a conditional on server side:
        if (is.null(input$calculate)) {
          output$observeReactiveValues <- renderUI({
            helpText(HTML("The current state is <code>is.null(input$calculate)</code>"))
          })
        }

        # if input$calculate is defined:
        if (input$calculate == 0){
          output$observeReactiveValues <- renderUI({
            helpText(HTML("The current state is <code>input$calculate == 0</code>"))
          })
        } 

        # if input$calculate is defined:
        if (input$calculate != 0 && busy$state == 1){
          output$observeReactiveValues <- renderUI({
            helpText(HTML("The current state is <code>input$calculate != 0 && busy$state == 1</code>"))
          })
        } 
        
        # if input$calculate is defined:
        if (input$calculate != 0 && busy$state == 0){
          output$observeReactiveValues <- renderUI({
            helpText(HTML("The current state is <code>input$calculate != 0 && busy$state == 0</code>"))
          })
        }
        
    })

    # Part III: create an observer on the state of actionButton "sleep"

    observe({ 
    
        input$sleep
        
        # if input$sleep is undefined:
        if (is.null(input$sleep)) {
          output$observeActionButton <- renderUI({
            helpText(HTML("The current state is <code>is.null(input$sleep)</code>"))
          })
        }
          
        # if input$sleep is defined:
        if (input$sleep == 0){
          output$observeActionButton <- renderUI({
            helpText(HTML("The current state is <code>input$sleep == 0</code>"))
          })
        }

        # if input$sleep is defined:
        if (input$sleep != 0){
          Sys.sleep(5)
          output$observeActionButton <- renderUI({
            list(
              helpText(HTML("The current state is <code>input$sleep != 0</code>."))
              , 
              helpText(HTML("You have just finished with <code>Sys.sleep(5)</code>. The actionButton only triggers once. Refresh your browser to reinitialize <code>input$sleep</code>."))
            )
          })
        }

    })

})

ui.R

# ui.R

shinyUI(
  pageWithSidebar(
    headerPanel("Use of observe with actionButtons, reactiveValues, and Sys.sleep() - Demo")
    , 
    sidebarPanel(
      actionButton(inputId = "calculate", label = "actionButton bound to reactiveValues")
      , tags$br(), tags$hr(), tags$br(), 
      actionButton(inputId = "sleep", label = "actionButton bound to Sys.sleep(5)")
      ,
      tags$hr()
      ,
      helpText("Basic Demo by Patrick Toche, 15 January 2014. In good faith but with no guarantees of correctness and/or elegance.")
    )
    , 
    mainPanel(
      h4("observe with reactiveValues conditioned on FIRST actionButton:")
    , 
    uiOutput("observeReactiveValues")
    , 
    tags$hr()
    , 
    h4("conditionalPanel that displays only after SECOND actionButton is actioned")
    , 
    conditionalPanel(condition = "input.sleep > 0"
        , wellPanel(
        uiOutput("observeActionButton")
        )
    )
    , 
    tags$hr()
    , 
    h4("Comment:")
    ,
    helpText(HTML("The <code>actionButton</code> is incremented by 1 each time it is actioned, so to keep track of several actions I created a reactiveValue that switches between 0 and 1 each time the actionButton is actioned"))
    )
  )
)

some people don't like my indentations, well they're ugly but they work for me ;-)